A wireless mesh network is a collection of wireless nodes or devices organized in a decentralized manner to provide range extension by allowing radios to be reached across multiple hops. Wireless mesh networks are based on self-configuring autonomous collections of portable devices that communicate with each other over wireless links having limited bandwidths. In a mesh network, communication packets sent by a source node thus can be relayed through one or more intermediary nodes before reaching a destination node. Mesh networks may be deployed as temporary packet radio networks that do not involve significant, if any, supporting infrastructure. Rather than employing fixed base stations, in some mesh networks each user node can operate as a router for other user nodes, thus enabling expanded network coverage that can be set up quickly, at low cost, and which is highly fault tolerant. In some mesh networks, special wireless routers also can be used as intermediary infrastructure nodes. Large networks can be realized using intelligent access points (IAPs), also known as gateways or portals, which provide wireless nodes with access to a wired backhaul or wide area network (WAN).
Enterprise-class, bandwidth-intensive applications, workgroup computing applications, and some wireless backhaul applications require throughputs larger than current Institute of Electrical and Electronics Engineers (IEEE) 802.11a/b/g technologies can provide. In addition to throughput, the IEEE 802.11n protocol significantly enhances the reliability and range of existing IEEE 802.11 networks. The standard defines procedures by which throughputs greater than several hundred Mega bits per second (Mbps) along with significant range improvements are possible. (Any IEEE standards or specifications referred to herein may be obtained at http://standards.ieee.org/getieee802/index.html or by contacting the IEEE at IEEE, 445 Hoes Lane, PO Box 1331, Piscataway, N.J. 08855-1331, USA.)
IEEE 802.11n provides Physical Layer (PHY) and Media Access Control (MAC) enhancements for high throughput modes with high data rates. For example, with a 800 nanosecond (nsec) guard interval, two spatial streams, and operating on a forty (40) Mega Hertz (MHz) bandwidth, data rates reach up to 270 Mbps. FIG. 1 illustrates the theoretically calculated MAC throughput for a 1500 byte packet size when using the IEEE 802.11n data rates. As illustrated, despite the fact that the PHY data rates go as high as 270 Mbps, the MAC layer throughput begins to saturate around 25 Mbps and attains a maximum value of only 38 Mbps. (Here “Nss” is defined as the number of spatial streams, Bandwidth (BW) is defined as the channel bandwidth in MHz).
At high data-rates, the carrier-sense multiple access with collision avoidance (CSMA/CA) mechanism becomes a bottleneck in transferring the high gains in the data rate to higher user throughput. Every frame transmitted by an IEEE 802.11 device has fixed overhead associated with the radio preamble and MAC frame fields that limit the effective throughput, even if the actual data rate was infinite.
FIG. 2 highlights the reason for low throughput in IEEE 802.11n. Although the data packets themselves are transmitted at the high data rates, control messages and headers are transmitted at low data rates (BSSBasicRateSet), thus resulting in significantly longer transaction air-times per packet. With high data rates, Physical Layer Convergence Protocol (PLCP) protocol data unit (PPDU) transmission is quick but inter-frame spacing, deference and backoff add significant overhead to overall packet transaction air-time. FIG. 2 illustrates the significant difference between packet Transaction Air-time and PPDU air-time. “PPDU Air-time” represents the transmission time of the data packet alone. “Transaction Air-time” represents the total air time including deference, transmission times of RTS, CTS, data packet and ACK, and the inter frame spaces.
Frame aggregation is a mechanism to alleviate the previously described deficiencies. With frame aggregation, once a station acquires the medium for transmission, potentially long packets can be transmitted without significant delays between transmissions and thus reducing the effect of MAC overhead and inefficiencies. IEEE 802.11n devices can send multiple frames per single access and supports two forms of frame aggregation: Aggregated Mac Service Data Unit (A-MSDU) and Aggregated Mac Protocol Data Unit (A-MPDU).
IEEE 802.11n does not specify any method or algorithm to decide when and how many packets can be aggregated to build an aggregated-frame. There is a need of dynamic and distributive methodology that computes when and how much to aggregate to take advantage of high data rates supported in wireless communication network.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.